How to use LDFLAGS in makefile

Question

I am new to Linux OS. I am trying to compile a .c file using a makefile. The math library has to be linked. My makefile looks like this:

CC=gcc
CFLAGS=-Wall -lm

all:client

.PHONY: clean
clean:
    rm *~ *.o client

When I run make, I get the following error:

"undefined reference to rint"

So it is not able to link the math library.

But when I compile explicitly using

gcc client.c -lm -o client

it successfully compiles.

So how should I change my makefile such that it works. I have already tried adding LDFLAGS=-lm. But I get the same error.

I should also add that when I run make, it expands to

gcc -Wall -lm client.c -o client

(notice that when I run gcc explicitly with -lm at the end, it works).

Answer 1

Your linker (ld) obviously doesn't like the order in which make arranges the GCC arguments so you'll have to change your Makefile a bit:

CC=gcc
CFLAGS=-Wall
LDFLAGS=-lm

.PHONY: all
all: client

.PHONY: clean
clean:
    $(RM) *~ *.o client

OBJECTS=client.o
client: $(OBJECTS)
    $(CC) $(CFLAGS) $(OBJECTS) -o client $(LDFLAGS)

In the line defining the client target change the order of $(LDFLAGS) as needed.